FIELD OF THE INVENTION
Laser initiation of explosives and pyrotechnics has held great potential promise for many years. Transmission of light energy from a laser through optical fibers allows reliable pyrotechnic initiation without the safety problems associated with hot bridgewire fired parts. Laser initiation has also held the promise of safe and reliable built-in testing (BIT) of the energy transmission system. It has also seemed possible to initiate laser fired cartridges with less energy than it takes to fire equally safe electrical initiators, and thus to reduce the size and weight of initiation systems.
In many ordnance initiation systems (such as space launch vehicles), the required functional reliability is such that it is necessary to check the integrity of as much of the system as possible immediately before launch. In other systems, such as emergency safety systems, intermittent system continuity checks are a prudent means of maintaining a high level of reliability. In typical present space launch vehicles, the continuity test function is performed manually by technicians on the launch pad while all other preparation activities are suspended. Built in test as envisioned in the present application verifies that each ordnance firing laser is connected to an optical initiator and that each optical initiator is connected to a BIT detector photodiode. This verification assures the user that lasers and initiators are connected and that none of the optical fibers are broken or otherwise disabled before the commencement of normal system operation. The capacity to perform continuity testing quickly, safely and automatically shortens the time between deciding to use a system and actually using it, eliminates the need to suspend other functions for an extended time and reduces the labor of preparation for system use.
Although some of the different advantages of laser initiators have been realized, they have generally not been realized together in a single embodiment. Systems that use the same optical fiber for energy transmission as for BIT suffer from ambiguity as a result of unwanted reflections of the transmitted light mixing with the desired BIT signal reflected from the initiator cartridge. Alternately, systems that use a separate BIT return fiber have improved signal to noise characteristics but suffer from increased size and complexity and are sensitive to a large number of alignment tolerances.
For example, U.S. Pat. No. 4,870,903 to Carel et al. discloses a laser driven initiator. However, Carel does not disclose any BIT mechanism to test the energy transmission system. Another laser driven ordnance apparatus, U.S. Pat. No. 5,404,820 to Hendrix, uses a complex scheme of diodes, splitters, and other apparatus to accomplish its BIT functions. Another system uses a "V" shaped path for the power from the laser, with the input power coming in one leg of the "V" and the BIT pulse going out of the other leg of the "V." This is a complex system to machine due to the tolerances involved.